In recent years, a touch detection device which is so called touch panel capable of detecting an externally-approaching object has been attracted attention. A touch panel is mounted on a display apparatus such as a liquid crystal display apparatus or integrated with a liquid crystal display apparatus so as to be provided as a display apparatus with a touch detection function.
As the externally-approaching object, a touch panel enabled to use, for example, a pen is known. By enabling the touch panel to use a pen, for example, a small area can be assigned or hand-written characters can be input. Various techniques to detect the touch by a pen are known. As one of the various techniques, an electromagnetic induction system is known. In the electromagnetic induction system, high accuracy and high handwriting pressure detection accuracy can be achieved, and a hovering detection function in a state in which an externally-approaching object is separated from the touch panel surface can be also achieved, and therefore, the system is a leading technique as the technique to detect the touch by a pen.
The touch detection technique using the electromagnetic induction system is described in, for example, Japanese Patent Application Laid-Open Publication No. H10-49301 (Patent Document 1), Japanese Patent Application Laid-Open Publication No. 2005-352572 (Patent Document 2), and Japanese Patent Application Laid-Open Publication No. 2006-163745 (Patent Document 3).
A touch detecting device capable of detecting a finger, etc., as the externally-approaching object is known. In this case, an object to be detected is different from the pen, and therefore, a system different from the electromagnetic induction system is employed for the touch detection technique. For example, systems of detecting optical change, resistance value change, or electric field change, caused by the finger touch, etc., are cited. As the system of detecting the electric field change among these systems, for example, a capacitive system utilizing a capacitance is cited. This capacitive system has a relatively simple structure and less power consumption, and therefore, is used for a portable information terminal, etc.